Progressive failure analysis of axially loaded single pile embedded in unsaturated soils based on LTM coupling with SDM

An analytical framework to analyze the progressive failure behavior of axially loaded single pile embedded in unsaturated soils is presented by means of the load transfer method (LTM) coupling with shear displacement method (SDM). In this study, the proposed DSC-based interface constitutive model and modified small-strain stiffness model undertake the role of load-transfer mechanism for the pile shaft and pile end, respectively, and the shear displacement method is adopted to take the soil deformation surrounding the pile shaft in consideration. This study adopts a stress loading approach in the solution process, differing from traditional strain loading methods, which involves assuming a segment of displacement at the pile end. By successively applying loading increments, the entire load–displacement relationship of the pile is accurately determined, effectively reproducing the authentic stress process of pile foundation, and analyzing the gradual failure processes of friction-dominated piles and end-bearing friction piles under varying suction conditions in unsaturated soil. Customized model piles with smooth, rough and ribbed surfaces and a stress-controlled servo system were developed to conduct static load tests on pile foundations in unsaturated sand-clay mixture and grey clay. Model parameters were calibrated through suction-controlled unsaturated ring shear tests. Finally, the validity of the solutions proposed in this study was verified by comparing the results of static load tests on smooth, rough and ribbed model piles. Subsequently, the effects of suction, interface dilation, and environmental factors on the load–displacement response were analyzed. The research findings of this study can provide a theoretical basis for the design of pile foundations with displacement control in unsaturated soil. © 2024 Elsevier Ltd